This invention relates generally to high frequency/high gain receivers and, more particularly, to circuitry utilized in such receivers to improve the leading and trailing edges of the received signal.
High frequency/high gain receiver systems are used in myriad of applications. For example, digital data communication equipment typically include a high frequency/high gain frequency shift keying (FSK) receiver. The digital data is received and demodulated as understood.
Sometimes the transmitted digital data can become distorted through intermediate stages of the receiver such that the square wave digital data is shaped more like a sine wave. If this is the case, the data must be reshaped to obtain useful bits of information.
Prior art systems have utilized comparators to square up the data bits. However in some receivers, e.g., FSK receivers, the direct current (DC) level of the data signal can drift away from the reference voltage of the comparator. This can be resolved by alternating current (AC) coupling but then the circuit can no longer handle long strings of bits of one polarity.
This problem was solved in one prior art wideband FSK receiver, the MC3356 receiver manufactured by Motorola Inc., using back to back clamping diodes across the inputs of a "floating" comparator. Although this scheme works quite well with large input signals and sufficient power supply voltages, it can not be used with low power supply voltages and signal levels due to the bias requirement of the two back to back diodes.
Hence a need exists for data shaping circuitry which overcomes the aforedescribed problems.